The JSON viewer in the Developer Tools uses insecure methods to create a communication channel for copying and viewing JSON or HTTP headers data, allowing for potential privilege escalation. This vulnerability affects Thunderbird < 45.7, Firefox ESR < 45.7, and Firefox < 51.
http://rhn.redhat.com/errata/RHSA-2017-0190.html
http://rhn.redhat.com/errata/RHSA-2017-0238.html
https://bugzilla.mozilla.org/show_bug.cgi?id=1297361
https://security.gentoo.org/glsa/201702-13
https://security.gentoo.org/glsa/201702-22
https://www.debian.org/security/2017/dsa-3771
https://www.debian.org/security/2017/dsa-3832
https://www.mozilla.org/security/advisories/mfsa2017-01/
https://www.mozilla.org/security/advisories/mfsa2017-02/